btrfs-progs: convert: simplify insert_temp_dev_extent()

This function requires parameters @slot and @itemoff to record where the
next item should land.

But this is overkilled, as after inserting an item, the temporary extent
buffer will have its header nritems and the item pointer updated.

We can use that header nritems and item pointer to get where the next
item should land.

This removes the external counter to record @slot and @itemoff.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

convert/common.c

@@ -459,37 +459,36 @@ static int setup_temp_chunk_tree(int fd, struct btrfs_mkfs_config *cfg,
 }
 
 static void insert_temp_dev_extent(struct extent_buffer *buf,
-				   int *slot, u32 *itemoff, u64 start, u64 len)
+				   struct btrfs_mkfs_config *cfg, u64 start, u64 len)
 {
 	struct btrfs_dev_extent *dev_extent;
 	struct btrfs_disk_key disk_key;
+	u32 slot = btrfs_header_nritems(buf);
+	u32 itemoff = get_item_offset(buf, cfg);
 
-	btrfs_set_header_nritems(buf, *slot + 1);
-	(*itemoff) -= sizeof(*dev_extent);
+	btrfs_set_header_nritems(buf, slot + 1);
+	itemoff -= sizeof(*dev_extent);
 	btrfs_set_disk_key_type(&disk_key, BTRFS_DEV_EXTENT_KEY);
 	btrfs_set_disk_key_objectid(&disk_key, 1);
 	btrfs_set_disk_key_offset(&disk_key, start);
-	btrfs_set_item_key(buf, &disk_key, *slot);
-	btrfs_set_item_offset(buf, *slot, *itemoff);
-	btrfs_set_item_size(buf, *slot, sizeof(*dev_extent));
+	btrfs_set_item_key(buf, &disk_key, slot);
+	btrfs_set_item_offset(buf, slot, itemoff);
+	btrfs_set_item_size(buf, slot, sizeof(*dev_extent));
 
-	dev_extent = btrfs_item_ptr(buf, *slot, struct btrfs_dev_extent);
+	dev_extent = btrfs_item_ptr(buf, slot, struct btrfs_dev_extent);
 	btrfs_set_dev_extent_chunk_objectid(buf, dev_extent,
 					    BTRFS_FIRST_CHUNK_TREE_OBJECTID);
 	btrfs_set_dev_extent_length(buf, dev_extent, len);
 	btrfs_set_dev_extent_chunk_offset(buf, dev_extent, start);
 	btrfs_set_dev_extent_chunk_tree(buf, dev_extent,
 					BTRFS_CHUNK_TREE_OBJECTID);
-	(*slot)++;
 }
 
 static int setup_temp_dev_tree(int fd, struct btrfs_mkfs_config *cfg,
 			       u64 sys_chunk_start, u64 meta_chunk_start,
 			       u64 dev_bytenr)
 {
 	struct extent_buffer *buf = NULL;
-	u32 itemoff = cfg->leaf_data_size;
-	int slot = 0;
 	int ret;
 
 	/* Must ensure SYS chunk starts before META chunk */
@@ -505,9 +504,9 @@ static int setup_temp_dev_tree(int fd, struct btrfs_mkfs_config *cfg,
 				       BTRFS_DEV_TREE_OBJECTID);
 	if (ret < 0)
 		goto out;
-	insert_temp_dev_extent(buf, &slot, &itemoff, sys_chunk_start,
+	insert_temp_dev_extent(buf, cfg, sys_chunk_start,
 			       BTRFS_MKFS_SYSTEM_GROUP_SIZE);
-	insert_temp_dev_extent(buf, &slot, &itemoff, meta_chunk_start,
+	insert_temp_dev_extent(buf, cfg, meta_chunk_start,
 			       BTRFS_CONVERT_META_GROUP_SIZE);
 	ret = write_temp_extent_buffer(fd, buf, dev_bytenr, cfg);
 out: